This invention relates, in general, to semiconductor devices, and more particularly, to field effect transistors having multiple vertically aligned channels controlled by active quantum well gates.
Compound semiconductor based heterostructure devices have been predicted to offer significant speed and power advantages over silicon devices. Compound semiconductor devices that have multiple vertically stacked channels allow greater functionality to be incorporated into smaller devices. Conventional field effect devices use a gate electrode located on a surface of the device. In these "surface gated" devices, the gate is a passive element of the transistor. Moreover, the transconductance of the field effect transistor depends on the distance from the gate to the centroid of charge on the channel. The magnitude of the transconductance decreases when the channel is far from the gate.
In a device having multiple vertically stacked channels, the gate exerts a stronger effect on the closest channel and the weakest effect on the furthest channel. This results in non-uniform performance among the channels of a multiple channel device, and complicates designs that require matched performance among the channels. What is needed is a semiconductor device which can provide more uniform performance among multiple vertically stacked channels.